The femoral head remnant in resurfacing arthroplasty.

The femoral head remnant was examined in six patients after Indiana resurfacing arthroplasty. Four hips failed by femoral neck fracture and two by acetabular loosening. Three of the four specimens that failed by fracture had total osteonecrosis, as assessed by histological criteria. The tissue did not evidence foreign body response to methyl-methacrylate, suggesting that osteonecrosis may have occurred at the time of resurfacing arthroplasty. Bony remodeling at the site of fracture indicates that fracture may have occurred through a weakened zone at the junction of viable and necrotic bone. In contrast, examination of the femoral specimens removed owing to acetabular loosening revealed viable bone, membrane formation and a foreign body reaction. The small number of specimens and lack of tetracycline labeling prohibit firm conclusions. These observations nevertheless suggest that resurfacing arthroplasty may, in some cases, cause osteonecrosis of the femoral head remnant, which may play a role in femoral neck fracture. Efforts should be made to obtain the femoral head remnant at autopsy and at revision surgery when indicated so that the state of the femoral head remnant after resurfacing arthroplasty and its role in the success or failure of the various procedures could be better understood.